MES

MES is a zwitterionic N-substituted aminosulfonic acid known as a Good’s buffer, active in the pH range 5.5-6.7 with a pKa of 6.10 at 25°C. MES is not absorbed through cell membranes, and it is essentially transparent to UV light1. MES is used as a running buffer for resolving very small proteins (ex: 13 kDa) on BIS-TRIS gels2.